The present invention relates to a control apparatus for a brushless motor and to a machine and apparatus using a brushless motor. The invention relates in particular to a control apparatus for controlling the speed of rotation of a brushless motor to a desired speed. This control apparatus may be used in an air conditioner for performing air conditioning in a room by controlling a brushless motor for driving a compressor and a blower in the air conditioner, a refrigerator for carrying out refrigeration by controlling a brushless motor for driving a compressor and a blower in the refrigerator, and a washing machine for carrying out the washing of clothes by controlling a brushless motor for driving an agitator and a spinning basket in the washing machine.
A brushless motor in which a permanent magnet rotor and a stator winding are combined typically is employed in an air conditioner, a refrigerator and a washing machine, etc. from an aspect of ease of maintenance.
In a drive control of the above stated brushless motor, it is necessary to carry out control in close relationship with the magnetic pole position of the rotor and the position of the stator winding to which electric power is suppled. To detect the magnetic pole position of the rotor, without use of a rotor position detection sensor, such as a Hall element etc, a sensorless position detection system is employed using a counter electromotive voltage, which is induced in the stator winding according to a mutual operation with the magnetic pole of the rotor, allowing the magnetic pole position of the rotor to be detected.
As a brushless drive apparatus in which the above stated rotor position detection system is employed, for example, there is a brushless motor drive apparatus described in Japanese application patent laid-open publication No. Hei 7-147793. In this brushless motor drive apparatus, a direct current voltage, which is outputted from a direct current power supply, is supplied to a stator winding of a brushless motor through an inverter circuit. A terminal voltage detection means produces a detection voltage by voltage dividing the terminal voltage of the stator winding of the brushless motor, and the detection voltage is inputted to a comparison circuit. The comparison circuit outputs a phase signal by comparing the detection voltage with a standard voltage.
And, on the basis of a pulse width modulation (PWM) signal PS generated from a pulse width modulation (PWM) signal generation circuit, a control apparatus generates a latch timing signal LS according to a latch signal generation circuit to perform a latch operation after a timing in which the above stated PWM signal PS changes from an "on" condition to an "off" condition. Even when an oscillation is generated in the terminal voltage of the stator winding, without being affected by such oscillation, the phase signal from the comparison circuit is latched in a latch circuit and the position detection signal can be obtained.